High-concentration nitrogen wastewater such as wastewater containing high-concentration, ammonium at about 3,000 ppm has high organism toxicity. As the result, it has been conventionally impossible in general to apply microbial treatment thereto. Therefore, in the case where the microbial treatment has generally been applied to wastewater containing nitrogen, ammonium concentration is as low as several hundred ppm.
Accordingly, the wastewater containing high-concentration ammonium of 3,000 ppm or more has been concentrated to about 1/10 with use of an evaporator as a physical treatment method, and then resultant concentrated solutions have been disposed as industrial wastes. The concentrated solutions were deemed as industrial wastes when employing the above-stated method of concentrating the wastewater with use of the evaporator and discharging them as industrial wastes from plants. Thus, this method has caused such problems as increase in industrial wastes from business establishments and air pollution due to the use of fuel such as heavy oil because the concentrated solutions as industrial wastes have generally been disposed by incineration.
The treatment method using the evaporator consumes a large quantity of energy and involves large plant equipment, which has caused a problem of large initial costs, running costs and maintenance costs.
As another prior art, a biological treatment method has been disclosed in Patent Document 1 (JP 2,000-308900 A). According to the biological treatment method in this prior art, degradation of treatment efficiency caused by nitrite-nitrogen is prevented to achieve stable treatment, wherein the nitrite-nitrogen is generated during treatment of wastewater containing high-concentration ammonium-nitrogen. Specifically, the biological treatment method includes a biological denitrification process using autotrophic bacteria resistant to nitrite-nitrogen, so that the nitrite-nitrogen is reduced to nitrogen gas before being removed from the wastewater.
As to the method of treating wastewater containing ammonium, there has been disclosed a nitrification tank, a denitrification tank and a UV oxidation tank, as well as treatments in the nitrification tank, a photocatalytic UV oxidation tank, the denitrification tank and the UV oxidation tank.
Another biological treatment method, as a prior art, is disclosed in Patent Document 2 (JP 3467671B).
This biological treatment method is classified to the nitrification and denitrification method. In the nitrification and denitrification method, organic wastewater within a raw water tank is sequentially fed to a denitrification tank and a nitrification tank by using a feeding pump, and the wastewater is circulated between both the tanks. As the result, ammonia-state nitrogen contained in the organic wastewater is reduced to nitrogen gas by biological nitrification and denitrification actions. Further, sludge and treated water are separated with use of a suction pump by a filtration film unit sunk in wastewater inside the nitrification tank.
The nitrification and denitrification method is characterized in that a pipe is branched on the way from the denitrification tank to the nitrification tank so that an end of the diverged pipe may be opened in the denitrification tank. As the result, part of organic wastewater fed from the denitrification tank to the nitrification tank is ejected into the organic wastewater in the denitrification tank. In other words, according to this nitrification and denitrification method, wastewater is fed to both the denitrification tank and the nitrification tank by using the feeding pump, and is circulated between both the tanks.
As yet another prior art, another biological treatment method is disclosed in Patent Document 3 (JP 3095620B).
In this biological treatment method, treatment is performed by a biological nitrogen rejection apparatus composed of a denitrification tank for receiving inflow of raw water containing organic matter, a nitrification tank for receiving inflow of denitrification tank mixtures from the denitrification tank, a nitrified liquid circulation channel for circulating a nitrified liquid of the nitrification tank to the denitrification tank, and a nitrification tank air diffuser placed inside the nitrification tank.
More specifically, the biological nitrogen rejection apparatus has a denitrifying bacteria immobilization support charging zone in the denitrification tank so as to catch and remove the suspended solids in the raw water flowing into the denitrification tank. Moreover, a raw water induction channel and a nitrified liquid circulation channel are linked to a lower position of the denitrifying bacteria immobilization support charging zone in the denitrification tank. A sludge hopper section is provided on the bottom section of the denitrification tank so as to accumulate the suspended solids caught and removed in the denitrifying bacteria immobilization support charging zone. A hopper air diffuser is provided in the sludge hopper section.
However, as described above, wastewater containing high-concentration ammonium at about 3,000 ppm has high organism toxicity, and therefore microbial treatment has not generally been applied. Specifically, the high-concentration ammonium wastewater has been treated by an incineration method or a concentration method because the high-concentration ammonium wastewater is too high in organism toxicity to undergo microbial treatment. Accordingly, the concentration method has such problems as heavy consumption of energy and increase in industrial wastes caused by concentrated solutions.
As yet another prior art, method and device for treatment using nanobubbles are disclosed in Patent Document 4 (JP 2004-121962 A).
This prior art utilizes such characteristics of nanobubbles as decrease in buoyancy, increase in surface area, increase in surface activity, generation of local high pressure fields, a surface active property and an antiseptic property which are attained by achievement of electrostatic polarization. Specifically, this prior art has disclosed that associating these characteristics with each other makes it possible to exert a fouling component adsorption function, a substance surface high-velocity cleaning function and an antiseptic function, so that advanced cleaning of various substances is conducted with low environmental load to purify the contaminated water.
As yet another prior art, a nanobubble generation method has been disclosed in Patent Document 5 (JP 2003-334548 A).
In this prior art, it has been disclosed that there is either step (1) for gasifying part of liquid by decomposition in liquids, step (2) for applying ultrasonic waves in liquids, or step (3) composed of a step for gasifying part of liquid by decomposition and a step for applying ultrasonic waves.
Although these two prior arts have certainly disclosed purification of contaminated water by using nanobubbles or removal of dirt on the surface of solids by using nanobubbles, they fail to disclose a technology to enhance efficiency of treatment and quality of treatment water at the time of treating waste gas and wastewater.